6-inch/40-caliber gun

6"/40 caliber Mark 4
USS Massachusetts (BB-2), 6-inch/40 caliber gun and crew.
Type	Naval gun
Place of origin	United States
Service history
In service	1885
Used by	United States Navy
Wars	Spanish–American War World War I
Production history
Designer	Bureau of Ordnance
Designed	1883
Manufacturer	U.S. Naval Gun Factory
Produced	1896 – 1905
No. built	72 (Nos. 133–196, 260–263, and 423–426)
Variants	Mark 4 Mod 0 – Mod 13 (no Mod 6)
Specifications
Mass	13,370 lb (6,060 kg) (without breech)
Length	Mod 0: 256.1 in (6,500 mm) Mod 1: 254.61 in (6,467 mm)
Barrel length	240 in (6,100 mm) bore (40 calibers)
Shell	105 lb (48 kg) naval armor-piercing
Caliber	6 in (152 mm)
Traverse	−150° to +150°
Rate of fire	As commissioned: 1.5 rounds per minute After 1906: 7.6 rounds per minute
Muzzle velocity	2,150 ft/s (660 m/s)
Effective firing range	9,000 yd (8,200 m) at 15.3° elevation 18,000 yd (16,000 m) at 30.2° elevation

The 6"/40 caliber gun Mark 4 (spoken "six-inch-forty-caliber") were used for the secondary batteries of the United States Navy's Indiana-class and Illinois-class battleships. They were also used as the main battery on the Cincinnati-class protected cruisers.^[1][2]